Anatomical and functional segments of the deltoid muscle

Abstract

Previous studies showed that the insertion of the intramuscular tendons of the deltoid muscle formed three discrete lines. The purpose of the present study was to establish a new dividing method of the deltoid muscle into various anatomical segments based on the distribution of the intramuscular tendons with their insertions (anatomical study). We further hoped to clarify the relationship between the anatomical segments and their activity pattern assessed by positron emission tomography with [18 F]-2-fluoro-deoxyglucose (FDG-PET; PET study). Sixty cadaveric shoulders were investigated in the anatomical study. Three tendinous insertions of the deltoid muscle to the humerus were identified. Then, the intramuscular tendons were traced from their humeral insertions to the proximal muscular origins. The extent of each anatomical segment of the muscle including its origin and insertion was determined through careful dissection. Six healthy volunteers were examined using FDG-PET for the PET study. PET images were obtained after exercise of elevation in the scapular plane. On the PET images, margins of each anatomical segment of the deltoid muscle were determined using magnetic resonance images. Then, the standardized uptake value in each segment was calculated to quantify its activity. The anatomical study demonstrated that the deltoid muscle was divided into seven segments based on the distribution of its intramuscular tendons. The PET study revealed that the intake of FDG was not uniform in the deltoid muscle. The area with high FDG intake corresponded well to the individual muscular segments separated by the intramuscular tendons. We conclude that the deltoid muscle has seven anatomical segments, which seem to represent the functional units of this muscle.

Morphology and a proposed model of innervation of the human deltoid muscle: a pilot study

“…The result obtained in the present study group (4 to 5 OT) may follow from the fact that branching OT were treated as 2 separate structures. This observation complies with those of Sakoma et al [34] on anatomical variations with double tendons in a single segment of the deltoid. Morgan et al [28] describe the DM insertion as 'long and broad'.…”

“…In descriptive anatomy and in clinical practice, it is accepted that the DM is divided into three parts, distinguished based on the location of their origins [29,31,37]. However, based on function, this division may not be completely accurate [34]. The division of the DM into segments was described by Albinus as early as in 1734 [1].…”

“…Leijnse et al [24] created a generic model of the origin and end tendons of the DM based on a structural analysis of 8 isolated deltoid muscles. On the basis of positron emission tomography scans of anatomical and functional DM segments, Sakoma et al [34] propose that the DM can be divided into 7 segments, separated by intramuscular tendons. A literature search reveals many different intramuscular tendon system models, which is reflected in a variety of terms: Audenaert and Barbaix [3] use the term 'septae', Klapper et al [21] describe such tendons as 'ligament-like bands', and 'Gray's anatomy' [37] refers to 'four intramuscular septa descending from acromion' which imbricate between 'three septa ascending from the deltoid tubercle', Lorne et al [27] describe the fibrous scaffolding of the DM as 'fibrous bands' and Palastanga et al [31] use the term 'tendinous slips'.…”

“…The division of the DM into segments was described by Albinus as early as in 1734 [1]. Literature accounts suggest that the DM may be divisible into segments on the basis of the intramuscular tendon system [3,24,27,34], or alternatively, based on interpretation of the results of functional studies (such as EMG or PET) conducted on live subjects [5,15,34,40]. Gorelick and Brown [15] performed a mechanomyographic assessment of contractile properties of 7 DM segments.…”

“…Recent studies have additionally suggested that the DM consists of a few anatomical and functional segments which may, to a large extent, be independently coordinated by the nervous system [3,5,15,34,40]. Specific issues concerning the relationship between the innervation and the muscle segments of the DM were not described, even in the latest research of Sakoma et al [34], from 2011.…”